Sintered porous iron article impregnated with oleic acid and an inhibitor for forming matching surfaces by friction

ABSTRACT

A process is disclosed for forming relatively moving metal parts with matching surfaces by preparing at least one part from porous sintered iron, impregnating the pores of the sintered iron part with oleic acid containing an inhibitor selected from Tenemene, BHA, BHT, or MTBHQ in an amount effective to inhibit the reaction between the iron and oleic acid at room temperature and subsequently bringing the parts into sliding contact until the heat developed at points of local high friction is sufficient to effect the reaction between iron and oleic acid. There is also disclosed a formed, porous sintered iron article with inhibited oleic acid in its pores.

United States Patent [191 Holman SINTERED POROUS IRON ARTICLEIMPREGNATED WITH OLEIC ACID AND AN INHIBITOR FOR FORMING MATCHINGSURFACES BY FRICTION [75] Inventor: John F. Holman, Ridgway, Pa.

[73] Assignee: Allegheny Ludlum Industries, Inc.,

Pittsburgh, Pa.

[22] Filed: Feb. 2, 1973 [21] Appl. No.: 329,271

[52] US. Cl 29/l82.5, 29/1821, 51/295, 117/134, 117/113, 75/200 [51]Int. Cl. B221 3/26, C23f 1/04 [58] Field of Search 117/134, 113; 51/295;156/7, 18; 29/1821, 182.5; 75/200 [56] References Cited UNITED STATESPATENTS 2,833,637 5/1958 Zucker et al. 51/295 3,471,277 10/1969Ackermann 51/295 2,307,343 l/1943 Whipple 117/134 Apr. 16, 1974 PrimaryExaminer-Carl D. Quarforth Assistant Examiner-B. I-lunt Attorney, Agent,or Firm-Vincent G. Gioia [5 7] ABSTRACT A process is disclosed forforming relatively moving metal parts with matching surfaces bypreparing at least one part from porous sintered iron, impregnating thepores of the sintered iron part with oleic acid containing an inhibitorselected from Tenemene, BHA, Bl-IT, or MTBHQ in an amount effective toinhibit the reaction between the iron and oleic acid at room temperatureand subsequently bringing the parts into sliding contact until the heatdeveloped at points of local high friction is sufficient to effect thereaction ,between iron and oleic acid. There is also disclosed a formed,porous sintered iron article with inhibited oleic acid in its pores.

9 Claims, No Drawings SINTERED POROUS IRON ARTICLE IMPREGNATED WITHOLEIC ACID AND AN INHIBITOR FOR FORMING MATCHING SURFACES BY FRICTIONBACKGROUND OF THE INVENTION Known powder metallurgy techniques permitdifficult metal shapes to be formed relatively easily. For example, ironcan be formed into shapes difficult to machine by pressing very smalliron particles into the desired shape and then heating the formed shapeto a temperature at which points of contact between adjacent particlesfuse. The resultant material is called sintered iron. It isdimensionally stable and very strong even though its structure isporous.

Sintered iron parts are frequently used in sliding contact with othermetal pieces in uses where it is necessary for the relatively movingsurfaces to be matched very closely. Even though powder metallurgytechniques can form pieces to very close tolerances, perfectly matchingsurfaces are difficult to obtain by the technique.

The porous nature of sintered iron has been taken advantage of torelieve this situation. When the pores of a sintered iron piece areimpregnated with oleic acid, a reaction between the iron and the acidoccurs and a soft reaction product results. When this reaction takesplace during sliding contact, matching surfaces can be obtained readily.However, oleic acid and powder metal iron react rapidly at roomtemperature so the process to achieve matched surfaces that employ thereaction between iron and oleic acid must be accomplished quickly, i.e.,the parts must be brought into sliding contact with each other beforesignificant quantities of the oleic acid in the pores have reacted withthe iron. As a consequence, the technique is difficult to use becauseoleic acid-impregnated sintered iron parts cannot be stored and becauseit is necessary to have impregnating equipment and machining equipmentin close proximity to one another. It is also difficult to incorporatesuch close timing into an ordinary industrial process.

THE INVENTION This invention provides a process that avoids the problemsset forth above. This invention is a process for forming matchingsurfaces between metal parts to be in sliding contact by making at leastone of the parts of sintered iron, impregnating the pores of that partwith oleic acid which contains Tenemene, BHA, BHT, or MTBHQ in an amounteffective to inhibit the reaction between iron and oleic acid at roomtemperature, and then bringing the parts into sliding contact until theheat generated by friction raises the temperature of local high frictionpoints to one at which iron and oleic acid will react.

The invention also is a formed sintered iron article that has its poresimpregnated with oleic acid containing an inhibitor selected fromTenemene, BHA, BHT, and MTBHQ in an amount effective to inhibit thereaction between iron and oleic acid.

Amounts of inhibitor in excess of 0.05%w are effective to inhibit thereaction and amounts in excess of 5.0%w have small incremental effect.Accordingly, it is preferred that the inhibitor be present in very smallamounts, in excess of about 0.05%wandpreferably in excess of about0.1%w, but that amounts in excess of It is presently thought that thesintered iron part im-.

pregnated with inhibited oleic acid is stable chemically as long as thetemperature is room temperature. Chemically stable means that oleic acidand iron do not react at a significant rate. When the impregnated partis brought into sliding contact, those portions of the contactingsurface that do not match the other surface are subjected to intensefriction over a very local area. The heat from this friction raises thetemperature above that at which the inhibitor is effective to retard orprevent the reaction between iron and oleic acid, and as a result theiron in the area of local high friction reacts rapidly with the oleicacid impregnated in the pores to form soft, amorphous iron oleate whichis washed away with lubricant or worn away but, in any event, isdisposed of benignly. When the surface aberration that caused the localhigh friction has been removed, the local high temperature will diminishand there will be no further reaction because the inhibitor again willbe effective to prevent iron from reacting with oleic acid. Since localconditions during sliding contact are not available for analysis orobservation, the foregoing hypothesis is merely suggested as themechanism by which the process of the present invention functions, butit is not intended to limit the claims to the accuracy of thishypothesis.

For the sake of brevity, certain trademarks and trade designations areused in this specification and the following claims. Each of these hasthe following meaning:

Tenemene is N,Nbis (1,4-dimethyl pentyl)-pphenylene diamine;

BI-IA is t-butyl hydroxy anisol;

BHT is t-butyl hydroxy toluene;

MTBl-IQ is mono-t-butyl hydroquinone.

DETAILED DESCRIPTION The present invention was employed in the manufac-.ture of rocker arm balls for use in internal combustion engines. Therocker arm balls function in sliding contact with a socket-like metalreceptacle. In use it is essential that the surface of the rocker armball be well matched to the surface of the receptacle.

The rocker arm balls were made from a material that was 98.7%w iron,0.18%w carbon, and the remainder miscellaneous materials includingsilicon, phosphorus, sulfur and oxygen. The material was in the form ofa fine powder having a particle size distribution on a weight basis asfollows:

% of Total trace This material was uniformly blended with 0.75%wgraphite and 0.75%w of a wax lubricant, the percentages being based onthe weight of powdered metal. The blended powder was then pressed intothe form of rocker arm balls until it had a nominal density of 6.0 g/cc,at which density it had sufficient green strength to be handled. Theparts were then heated to about 2,000F in an inert gas atmosphere atwhich temperature a sintered metal structure was formed. The sinteredmetal structure was cooled in the oven to about 1,550F after which itwas quenched in a conventional quench oil. At this point the sinterediron piece had approximately the same dimensions and same density as thegreen form.

The quenched rocker arm balls were cleaned by a technique which providedavailable pore volume for the subsequent impregnation with inhibitedoleic acid.

The balls thus prepared were divided and some of them were immersed inoleic acid, while others were immersed in oleic acid containing variousamounts of various inhibitors. The total pore volume of the balls wassuch that a maximum of 0.4 grams of impregnant, consisting of quench oiland oleic acid, could be taken up per ball. In all cases of ballsprepared as described above, about 44%w of the maximum impregnant wastaken up as oleic acid. The acid impregnated balls were exposed to openair at room temperature for three weeks after which they were analyzedto determine their free oleic acid content. The results of theseanalyses are set forth in Table I:

The rocker arm balls containing inhibited oleic acid were heated in thepresence of an indicator and it was found that the inhibitor in allcases was temperature sensitive. At temperatures higher than 200F thereaction between iron and oleic acid proceeded at a rapid rate eventhough an inhibitor was present.

The impregnated iron articles of this invention may be employed directlyin accordance with the process of the invention by bringing the matingsurfaces together with sufficient force and in sliding contact to createfriction that will raise the temperature of local surface aberrationsabove the effective temperature of the inhibitor. Surfaces such asvalves and valve seats to be used in a cold environment may be soprepared. If oleic acid is not wanted in the final structure, it may beremoved by conventional methods such as immersing the part in a solventor employing the solvent with ultrasonic vibrations.

A particularly useful embodiment of the invention is to install theoleic acid-impregnated part in a final assembly and to have the surfacesto be in sliding contact matched during the operation of the finalassembly. As an example, the rocker arm balls described above may be soemployed. In the assembly of an internal combustion engine, oleicacid-impregnated sintered iron rocker arm balls may be assembled in thenormal manner and the process for producing matched surfaces may beeffected when the finally assembled internal combustion engine is putinto operation. When the engine is operated, preferably slowly underbreak-in conditions, the sliding contact between the rocker arm ballsand their sockets will produce virtually perfectly matching surfaces.Additionally, the normal circulation of lubricant will cause any ironoleate formed to wash way, eventually being captured in the oil filter,while the impregnated oleic acid is soluble in oil and will be removedfrom the rocker arm balls when its effect is no longer desirable.

What is claimed is:

1. An article of manufacture comprising a porous, sintered iron articlehaving in the pores thereof oleic acid containing an inhibitor selectedfrom the group consisting of N,N'bis (l, 4-dimethyl pentyl)-pphenylenediamine, t-butyl hydroxy anisol, t-butyl hydroxy toluene, andmono-t-butyl hydroquinone in an amount effective to inhibit the reactionbetween iron and oleic acid at room temperature.

2. The article of claim 1 wherein the oleic acid contains at least0.05%w of inhibitor.

3. The article of claim 1 wherein the inhibitor is N,N'bis (l,4-dimethyl pentyl)-p-phenylene diamine.

4. The method for producing relatively moving parts with matchingsurfaces comprising:

A. manufacturing one of said parts of porous, sintered iron,

B. impregnating the pores of the sintered iron part with oleic acidcontaining an inhibitor selected from the group consisting of N,N'bis l,4-dimethyl pentyl)-p-phenylene diamine, t-butyl hydroxy anisol, t-butylhydroxy toluene, and mono-t-butyl hydroquinone in an amount effective toinhibit the reaction between iron and oleic acid at room temperature,and

C. placing the relatively moving parts in contact and effecting relativemotion for a time and under conditions such that points of high frictionwill be at a temperature at which the reaction between iron and oleicacid is effected.

5. The method of claim 4 wherein the oleic acid contains at least 0.05%wof inhibitor.

6. The method of claim 4 wherein the inhibitor is N,N'bis (l, 4-dimethylpentyl)-p-phenylene diamine.

7. The method for producing a sintered iron article suitable for movingengagement with another metal part comprising:

A. preparing a porous sintered iron article,

B. cleaning the article to provide open pore volume,

and

C. impregnating the pores in the article with oleic acid containing aninhibitor selected from the group consisting of N,N'bis (1, 4-dimethylpentyl)- p-phenylene diamine, t-butyl hydroxy anisol, tbutyl hydroxytoluene, and mono-t-butyl hydroquinone in an amount efi'ective toinhibit the reaction between iron and oleic acid at room temperature.

8. The method of claim 7 wherein the oleic acid contains at least 0.05%wof inhibitor.

9. The method of claim 7 wherein the inhibitor is N,N'bis (1, 4-dimethylpentyl)-p-phenylene diamine.

2. The article of Claim 1 wherein the oleic acid contains at least0.05%w of inhibitor.
 3. The article of claim 1 wherein the inhibitor isN,N''bis (1, 4-dimethyl pentyl)-p-phenylene diamine.
 4. The method forproducing relatively moving parts with matching surfaces comprising: A.manufacturing one of said parts of porous, sintered iron, B.impregnating the pores of the sintered iron part with oleic acidcontaining an inhibitor selected from the group consisting of N,N''bis(1, 4-dimethyl pentyl)-p-phenylene diamine, t-butyl hydroxy anisol,t-butyl hydroxy toluene, and mono-t-butyl hydroquinone in an amounteffective to inhibit the reaction between iron and oleic acid at roomtemperature, and C. placing the relatively moving parts in contact andeffecting relative motion for a time and under conditions such thatpoints of high friction will be at a temperature at which the reactionbetween iron and oleic acid is effected.
 5. The method of claim 4wherein the oleic acid contains at least 0.05%w of inhibitor.
 6. Themethod of claim 4 wherein the inhibitor is N,N''bis (1, 4-dimethylpentyl)-p-phenylene diamine.
 7. The method for producing a sintered ironarticle suitable for moving engagement with another metal partcomprising: A. preparing a porous sintered iron article, B. cleaning thearticle to provide open pore volume, and C. impregnating the pores inthe article with oleic acid containing an inhibitor selected from thegroup consisting of N,N''bis (1, 4-dimethyl pentyl)-p-phenylene diamine,t-butyl hydroxy anisol, t-butyl hydroxy toluene, and mono-t-butylhydroquinone in an amount effective to inhibit the reaction between ironand oleic acid at room temperature.
 8. The method of claim 7 wherein theoleic acid contains at least 0.05%w of inhibitor.
 9. The method of claim7 wherein the inhibitor is N,N''bis (1, 4-dimethyl pentyl)-p-phenylenediamine.